12/03/2009 @ 6:50PM

Self-Healing Antennas

The antenna invented by Michael Dickey and Gianluca Lazzi sounds more like silly putty than something that can transmit and receive wireless signals.

Says Lazzi: “You can change its length, you can bend it to conform to whatever surface you like, you can even squish it and it goes back to its original form.”

Lazzi, chair of the department of Electrical and Computer Engineering at the University of Utah, and Dickey, a chemical engineer at North Carolina State University, have created an antenna made of a metal alloy that is liquid at room temperature. They inject the alloy into thin tubes called microchannels designed into whatever they want to hold the antenna.

“The wire itself is a liquid so its mechanical properties are defined by the encasing material, which could be lots of things–a rubber band, bathroom caulk,” says Dickey. “Then the antenna is like the caulk or the rubber band, and it snaps back.”

Because the signals that antennas pick up depend on their shape, this antenna can be tuned to a huge range of frequencies just by stretching it. The hope is this kind of flexible, tunable antenna could be used in flexible electronics, in biomedical devices, in military applications and as a sensor embedded in construction materials.

Dickey’s work centers mostly around chemical microchip fabrication techniques while Lazzi, an antenna expert, is working on biomedical applications for antennas like ones that can be used in an artificial retina to receive signals from a camera outside the body.

Dickey approached Lazzi after a talk Lazzi gave in North Carolina and wondered if it would be worthwhile to try to make an antenna out of a liquid. “We started working on them and it turned out the properties of the antennas are remarkably good,” says Lazzi.

Antennas are often made of copper because copper is a good conductor of electricity. They are shaped to interfere with specific frequencies of radiation, like radio waves that carry screaming talk show hosts or cellphone text messages destined for the tabloids. When the right frequency of radiation hits the antenna, it generates electric currents that the electronic guts of the device decode.

This new antenna is an alloy of gallium and indium, which is a liquid at room temperature. But unlike other liquid metals like mercury, this alloy doesn’t bead up. Instead it spreads out like paint and the outer portions react with oxygen to create a skin.

Dickey compares it to crème brulee. “That’s the trick in all of it,” he says. “The skin allows you to form mechanically stable structures, but if you bend or rupture it, liquid will seep out and create a new skin.”

This also makes it easy to connect to. Instead of having to solder it like a conventional antenna, you can just jam a wire into it and make an electrical connection.

A big limitation is price. The indium in the alloy can likely be replaced by a cheaper alternative, like tin, but the gallium is crucial–and expensive. This antenna won’t be destined for your cell phone or your AM radio. “Those antennas are cheap and they really work pretty well,” Dickey says.

But it might offer enough advantages to find its way into more niche applications. The antenna could be incorporated into a device that could stretch or compress the antenna in order to change the range of radio frequencies it can pick up or emit (antennas work both ways).

It could be incorporated into a bridge, for example, and act like a sensor that could provide information about how far and in what ways the bridge is stretching or bending.

This ability to tune the antenna could be helpful as more wireless devices use more and more of the available spectrum of frequencies. Designers could develop devices that, instead of being made to work at only one small section of the spectrum, could instead scan for whatever is available and use that.

“Everybody wants a piece of frequency, but we are running out,” says Lazzi. “[With our antenna] any time there is spectrum free, you could go and use that part. You could adapt the antenna to whatever.”